If you have a large number of colleagues from whom you need to receive files, there is an alternative to sending out a lot of separate invites: you can set up an envelope. The concept is similar to a self-addressed stamped envelope: you give it to someone, and he or she only needs to fill it and send it, and it'll reach your in-box. They don't even need to create their own account, so the sender can be someone with or without an SUID.
To create an envelope, you must first create your own MSS account. Then, submit a help request specifying that you'd like to set up an envelope for MSS. Someone at IRT Information Security Services will work with you to complete the process, and when finished, you will receive a custom URL that points to your envelope. You can give the URL to anyone who needs to send you a file, and you will receive an email with a link to download it, just like a regular MSS message.
(In order to continue to receive files through an envelope, you should make sure your account remains active. Accounts expire after 30 days of inactivity, so make sure to log in occasionally..)